This invention relates generally to tufting machines for forming fine gauge cut pile fabric and more particularly to improved knife blocks for mounting the knives in such machines and to the method of producing the knife blocks.
In cut pile tufting machines an oscillating knife cooperates with an oscillating hook or looper to cut the loop of yarn that has been seized by the looper from a corresponding needle. It is conventional in such machines for the knife to be supported and retained in a knife block carried by an oscillating knife bar. Examples of the known knife blocks are illustrated in Card U.S. Pat. No. 3,277,852; Cobble et. al. U.S. Pat. No. 3,386,398; Cobble U.S. Pat. No. 3,604,379; and Bonner U.S. Pat. No. 3,788,245. However, each of these patents discloses a knife block limited to mounting one or two knives only. In the aforesaid patents illustrating the mounting of two knives, the knives are received in side by side relationship in two longitudinal channels spaced apart by a central longitudinal web formed generally integral with a pair of longitudinally extending oppositely facing spaced flanges undercut to form grooves. The grooves together with the surfaces of the web define the knife receiving channels. The thickness of the web provides the required structural strength to the knife blocks to resist twisting and bending when the knives are positioned and secured in the channels.
The gauge of a pile fabric is determined by the spacing between adjacent gauge parts, i.e., the needles, loopers and knives. Thus, the spacing between a pair of knives mounted in a knife block is a measure of the gauge of the cut pile fabric produced. In fine gauge cut pile fabric, i.e., 1/10 gauge and smaller, the spacing between a point on one knife to the corresponding point on an adjacent knife is respectively 0.1 inch and smaller. Thus, in the two knife receiving knife blocks of the prior art the thickness of the web to accomodate a knife of a 1/10 gauge machine would be 0.1 inch minus the thickness of one knife. Moreover, the thickness of the entire block is such that the shaft supporting the block in the oscillating knife bar is too small to support the load on the block and tend to break by shearing. Furthermore, the location of the knife bar and the proximity of the adjacent blocks makes the assembly of the multiplicity of blocks difficult. One theoretical solution for obtaining a larger block supporting shaft is to mount two or more knives on each side of the central knife block web. However, the extremely thin web section results in excessive bending and twisting of the web upon insertion and assembly of replacement knife blades into a block remaining in the machine.